The following studies on Chelydra serpentina are planned for the coming grant period: 1 - Analysis of rejection of limbs which arose from allogeneic limb buds grafted at an early embryonic stage. 2 - Second and third set responses of skin grafts following allogeneic limb bud transplantation. 3 - Morphology and cytochemistry of normal Chelydra blood corpuscles and study of the blood and marrow of experimental animals. 4 - Influence of temperature during incubation on sex differentiation. 5 - Analysis of abnormalities produced by thalidomide, captan and malathion.